1. FIELD OF THE INVENTION
The present invention relates to brake systems. More specifically, it relates to a disc brake system having pelletized brake lining material.
2. DESCRIPTION OF THE PRIOR ART
In prior art disc brake assemblies, generally a C-clamp caliper housing is positioned so as to grip opposite sides of the rotor. The caliper is rigidly anchored to the vehicle to absorb the torque loads while the rotor is fastened to the wheel hub or axle and rotates with it. Pads of friction material, usually metal backed, are floatably mounted to the caliper legs which are actuated when braking is desired to pinch the rotor. The braking friction forces are absorbed by the pads which are restrained by the metal backing and the caliper housing. Brake actuation is normally accomplished through hydraulic slave cylinders whose pistons abut the metal backing of the friction pads.
The disadvantages of the prior art disc brake assemblies are numerous, including a tendency to exhibit uneven lining wear causing squeaky brakes, the floating parts must be free of dirt, and corrosion of the pads can cause the pads to become jammed into a fixed position and thus are unable to float. Other problems include the need for periodic replacement of the pads, the difficulties inherent in attaching an emergency brake to a disc pad brake system, the heavy weight of the assemblies, the difficulties in providing higher friction lining material brake pads to permit increased brake torque absorption without sacrificing brake lining pad life (i.e. for aggressive brake applications) and cost. These disadvantages will be discussed more fully hereinafter.
In disc brake assemblies, the brake pads, when they are brought into frictional contact with the associated disc, must be held against rotation in some manner. That is, the torque forces must be transmitted from the brake pads to a stationary member. If this force is transmitted from either one or both of the brake pads to the actuating caliper assembly and then to an associated stationary member, the caliper assembly, due to tolerance buildup, has a tendency to twist because of misalignment which is caused by the necessary production tolerances between the caliper and the stationary member and due to an inherent deflection of the stationary member itself. The resultant twisting of the caliper will cause uneven lining wear. In many instances, this type of torque-absorbing arrangement may add unnecessary weight to the caliper assembly. In addition, if the brake pads are not free of dirt and corrosion, the pads will not be able to slide freely within the caliper. This will lead to uneven lining wear on the pads causing squeaky or noisy brakes.
Since the brake lining material of the brake pads has a finite thickness, eventually the lining material wears off and the metal backing plate rubs against the disc. This can cause severe damage to the rotor and, in extreme cases, can destroy the rotor. In order to prevent rotor scoring from occurring, periodic inspection and eventual replacement of the brake lining pads is required. In some instances, it has been possible to use modified brake lining compositions to extend the life of the brake lining pads. However, extended life brake lining pads are usually accomplished by a tradeoff of superior friction characteristics for better life. Even with extended life brake lining pads, the periodic inspection and replacement of the brake lining pads is only delayed and replacement of the pads is ultimately required.
Finally, conventional disc brake systems are inherently complex and costly to manufacture due to the close production tolerances required. Another factor adding to the manufacturing costs is the number of associated parts.
To summarize briefly, the disadvantages of the prior art brake disc pad assemblies are as follows: the uneven lining wear; the squeaky and noisy operation; the need for periodic replacement of the pads; the need for the pads to float freely; the heavy weight of the assemblies; the cost and the difficulties of providing higher friction lining material brake pads to permit increased brake torque absorption without sacrificing brake pad life or cost.